纤维复合材料层合板的层间增韧及低速冲击研究

发布时间：2018-03-05 01:13

本文选题：层合复合材料　切入点：尼龙无纺布　出处：《山东大学》2015年硕士论文　论文类型：学位论文

【摘要】：近年来复合材料的应用量呈逐年增长趋势,在航空航天领域的应用尤为广泛,其中碳纤维增强树脂基复合材料(CFRP)由于其自身的特殊优势,尤其是轻量化和高强度,作为结构件得到大量应用,显著改善了航空航天器的燃油经济性能。同时CFRP在其他产品领域,包括民用交通工具、建筑、体育器材等,也得到一定应用。但其层合结构的特点导致层间力学性能与纤维铺层相比较弱,容易出现分层损伤,并进一步降低结构的整体力学性能。另一方面在服役过程中,复合材料层合板遭受低速冲击的概率非常高,并且一般不会在冲击表面留下目视可检的损伤。但在层合板结构内部可能形成基体开裂、层间分层,这些损伤会严重降低层合板的剩余强度,特别是横向面内的压缩强度。上述损伤的产生会留下潜在的安全隐患,因此开展层合结构复合材料的典型破坏及层间增韧研究具有重要的理论意义和应用价值。本文通过引入“离位”增韧技术,使用尼龙无纺布(Polyamide Non-woven Fabric,PNF)增韧层,实现了对层合板Ⅰ型、Ⅱ型断裂韧性的大幅提高,有效抑制了分层损伤的产生。采用双线性内聚力模型(Cohesive Zone Model,CZM)代表增韧区力学行为,以基于连续损伤力学模型进行二次开发的材料本构来表征铺层的力学特性,通过商业有限元软件ABAQUS建立了双悬臂梁弯曲实验和端部切口实验的有限元模型,开展相关数值分析,并研究了关键参数对复合材料整体力学性能的影响。研究发现随着增韧区强度的增加,分层的临界载荷与临界位移有增大趋势。而随铺层厚度的增加,除分层扩展的临界位移呈减小趋势外,初始斜率、峰值载荷和裂纹扩展距离均增加。此外,两种断裂的初始斜率和峰值载荷都随预制裂纹长度增加而减小,但Ⅰ型分层临界位移随预制裂纹长度的增加逐渐增大,而Ⅱ型分层临界位移随预制裂纹长度的增加先减小后增大。在准静态力学研究的基础上,本文针对低速冲击问题开展了动态力学研究。首先针对国内民用量较大的C1500材料体系层合板,开展低速冲击实验及超声C扫描、冲击后压缩强度(CAI)测试等相关损伤检测,并进一步探讨了层合板厚度、铺层方式对其冲击响应和损伤的影响。研究发现层合板厚度一定时,相对于[45/0/-45/90]2s试样,[0/90]4s和[45/-45]4s试样的冲击载荷更低,且这两个试样具有更长的冲击行程。在6.67 J/mmm的标准冲击能量下,损伤面积随试样铺层数的减小明显减小。[45/-45]4S层合板的损伤面积更接近于[45/0/-45/90]2S,而[0/90]4S层合板的损伤小于前两者。同时C1500材料体系的CAI在160-180 MPa左右。最后结合实验与数值分析方法,开展尼龙无纺布层间增韧纤维复合材料的低速冲击破坏研究,揭示了碳纤维复合材料在低速冲击下的力学行为及其损伤机理,并进一步研究了增韧区厚度和强度对复合材料整体冲击性能的影响,对增韧层设计提出了合理建议。研究发现基体断裂和分层是层合板遭受低速冲击时最主要的损伤模式。随着增韧区厚度的增加,试样的初始刚度和峰值载荷都明显减小,且试样的承载能力受层间剪切强度影响更大。同时随着增韧区厚度的减小或强度的增加,冲击导致的试样损伤面积显著降低。
[Abstract]:In recent years, application of composite materials is increasing year by year, in aerospace applications is particularly wide, the carbon fiber reinforced epoxy resin composites (CFRP) because of its own advantages, especially lightweight and high strength, widely used as structural parts, improve the fuel economy performance of aircraft and spacecraft. At the same time, CFRP in other product areas, including civilian vehicles, buildings, sports equipment, etc., are used. But the laminated structure characteristics of the interlayer and mechanical properties of fiber layer compared to weak, are susceptible to delamination, and further reduce the overall mechanical performance of the structure. On the other hand, in the course of service and the composite laminates subjected to the probability of low velocity impact is very high, and generally do not leave visual inspection in shock damage surface. But in the internal laminate structure may form a matrix cracking, Delamination damage that would seriously reduce the residual strength of composite laminates, especially the compression strength of transverse plane. The damage will have potential safety hazards to stay, so it has important theoretical significance and application value to carry out research on toughening laminated structure of composite materials of typical damage and interlayer. In this paper, through the introduction of the "from" toughening technology, the use of nylon non-woven (Polyamide Non-woven Fabric, PNF) toughening layer, the laminated type I, type II fracture toughness is greatly improved and can effectively restrain the delamination damage. Using bilinear cohesive zone model (Cohesive Zone Model, CZM) on behalf of the district to the mechanical behavior of toughening, constitutive to characterize the mechanical properties of layer two development materials based on continuum damage mechanics model, using commercial finite element software ABAQUS to establish the double cantilever beam bending test and end the incision The finite element model, carry out the relevant numerical analysis, and studied the influence of key parameters on the mechanical properties of composite materials. The study found that with the increase of the strength of the toughening zone, critical load and critical displacement stratification increases. With increasing thickness, in addition to the critical displacement of delamination growth tends to decrease, the initial slope the peak load, and crack propagation distance were increased. In addition, the initial slope and the peak load of two kinds of fracture with prefabricated crack length increases, but the type of critical displacement with increasing stratification prefabricated crack length increases gradually, while type II critical displacement with increasing stratification prefabricated crack length decreased and then increased. On the basis of study on quasi static mechanics, aiming at the problem of low velocity impact was studied. The dynamic mechanical material system of C1500 laminates for domestic large amount, to carry out the real impact Inspection and ultrasonic C scan, compression strength after impact (CAI) injury related testing, and further discusses the laminate thickness, affecting the response of layers on the impact and damage. The study found that the thickness of laminates when compared with [45/0/-45/90]2s samples, [0/90]4s and 45/-45]4s [sample impact load is lower, and the impact of stroke the two sample is longer. In 6.67 J/mmm standard impact energy, reduce the damage area with the number of layers of the specimen decreases the damage area of.[45/-45]4S laminates is closer to [45/0/-45/90]2S, while the [0/90]4S laminate damage is less than the former two. At the same time, the material system of C1500 CAI was about 160-180 MPa. Finally, experimental and numerical failure analysis method, research on interlayer toughening of nylon non-woven fiber composite low velocity impact, reveals the mechanical behavior of carbon fiber composites under low velocity impact And the damage mechanism, and further study the influence of thickness and strength of toughened zone on the overall impact performance of composite material, the reasonable suggestion on toughening layer is proposed. The study found that matrix fracture and delamination are the main damage mode of the laminate subjected to low velocity impact. With increasing the thickness of the sample Zone toughness, initial stiffness and the peak load are decreased, and the sample capacity is affected by the interlaminar shear strength is larger. With the increase of toughening zone thickness or the decrease of the intensity of the sample, that the impact damage area decreased significantly.

【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB332

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